Given the rationale, provide a reasonable question and answer. Step-by-step reasoning process: To answer the question, consider the following: Osteochondritis dissecans (OCD or OD) is a joint disorder in which cracks form in the articular cartilage and the underlying subchondral bone.
 The question and answer:
Osteochondritis dissecans (OCD or OD) is a joint disorder in which cracks form in the articular cartilage and the underlying subchondral bone. OCD usually causes pain and swelling of the affected joint which catches and locks during movement. Physical examination typically reveals an effusion, tenderness, and a crackling sound with joint movement.

What is an ocd lesion of the knee?
The answer is a joint disorder in which cracks form in the articular cartilage and the underlying subchondral bone